The vowel quality in some diphthongs of Swabian (an upper german dialect) was determined by measurement of first and second formant values. A minimal contrast could be shown between two different diphthong qualities /Ae/ and /«i/, where for Standard German only one is assumed, viz. /ai/. The two diphthong qualities differ only slightly in onset and offset vowel quality, so a better understanding of their relationship was expected from an examination of their dynamic aspects. Our preliminary results suggest that there is indeed a difference in the temporal structure of the two diphthongs.